Object detection apparatus

ABSTRACT

In an object detection apparatus, a first region definition unit defines a first object region including a first detection point representing a relative position of a first object detected by a millimeter-wave radar with respect to a reference point in an XY-plane. An X-axis direction of the XY-plane is a vehicle widthwise direction, and a Y-axis direction of the XY-plane is a vehicle lengthwise direction. A second region definition unit defines a second object region including a second detection point representing a relative position of a second object detected based on a captured image with respect to the reference point. A region size modification unit modifies the size of the first region in the presence of axial misalignment of the radar. A determination unit determines that the first and second objects are the same if there is an overlap of the first and second object regions in the XY-plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority fromearlier Japanese Patent Application No. 2014-193889 filed Sep. 24, 2014,the description of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to techniques for detecting objects usinga radar and a camera.

BACKGROUND ART

Vehicle collision avoidance systems are required to accurately detectobjects, such as a vehicle other than an own vehicle that is a vehiclecarrying the system and a pedestrian. For example, a vehicle collisionavoidance system as disclosed in Patent Literature 1 is configured todetect objects using a radar and a camera. More specifically, thedisclosed vehicle collision avoidance system uses a millimeter-waveradar and a stereoscopic camera separately, and if a positionalrelationship between an object detected by the millimeter-wave radar andan object detected by the stereoscopic camera meets a predeterminedcriteria, determines that these objects are the same.

CITATION LIST Patent Literature

[Patent Literature 1] JP-A-2014-122873

SUMMARY OF THE INVENTION Technical Problem

In the above vehicle collision avoidance system, however, a sensormounting angle may deviate from a predetermined mounting angle, whichmay cause vertical or horizontal axial misalignment of the sensor.Insufficient axial misalignment correction may result in reduced objectidentification accuracy.

In consideration of the foregoing, exemplary embodiments of the presentinvention are directed to providing an object detection apparatuscapable of accurately determining whether or not objects detected usinga radar and a camera are the same even in the presence of axialmisalignment.

Solution to Problem

In accordance with an exemplary embodiment of the present invention,there is provided an object detection apparatus mounted in a vehicle,including: a first region definition unit configured to define a firstobject region including a first detection point, the first detectionpoint representing a relative position of a first object detected basedon information acquired by a radar with respect to a reference point inan XY-plane, the reference point representing a position of the vehicle,an X-axis direction of the XY-plane being a vehicle widthwise direction,and a Y-axis direction of the XY-plane being a vehicle lengthwisedirection; and a second region definition unit configured to define asecond object region including a second detection point, the seconddetection point representing a relative position of a second objectdetected based on an image captured by a monocular camera with respectto the reference point in the XY-plane.

The apparatus further includes: an axial misalignment detection unitconfigured to detect the presence or absence of axial misalignment thatrepresents a deviation of a direction of an axis of the radar from areference direction; a region size modification unit configured to, inthe presence of the axial misalignment, modify the size of the firstregion; and a determination unit configured to determine whether or notthere is an overlap of the first and second object regions in theXY-plane, and if it is determined that there is an overlap of the firstand second object regions in the XY-plane, then determine that the firstand second objects are the same.

With the object detection apparatus configured as above, in the presenceof axial misalignment, the determination as to whether or not there isan overlap of the first and second object regions in the XY-plane can bemodified by modifying the size of the first region. This configurationenables a more accurate determination as to whether or not the first andsecond objects are the same.

The above and other objects, features and advantages of the presentinvention will be readily apparent and fully understood from thefollowing detailed description of preferred embodiments, taken inconnection with the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram of a collision mitigation apparatus inaccordance with one embodiment of the present invention;

FIG. 1B is a functional block diagram of a collision mitigation ECU;

FIG. 2 is a flowchart of collision mitigation processing to be performedin the collision mitigation ECU;

FIG. 3 is a plan view of error regions when no axial misalignment isoccurring;

FIG. 4 is a flowchart of axial misalignment correction processingincluded in the collision mitigation processing;

FIG. 5 is a graph of width of an error region versus relative speed;

FIG. 6 is a plan view of error regions for a negative relative speedwhen axial misalignment is occurring;

FIG. 7 is a plan view of error regions for a positive relative speedwhen axial misalignment is occurring;

FIG. 8 is a graph of extent of an error region versus axial misalignmentangle; and

FIG. 9 is a plan view of error regions when a rightward axialmisalignment is occurring.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

(Configuration)

An collision mitigation apparatus 1 in accordance with one embodiment ofthe present invention is an apparatus mounted in a vehicle (hereinafterreferred to as an own vehicle), such as a passenger car, and configuredto detect an object (that is an object, such as a vehicle other than theown vehicle or a pedestrian) using a radar and a camera image, and incases where the own vehicle is likely to collide with the object,perform control operations, such as braking the own vehicle, to avoidthe collision or mitigate the impact of any possible collision betweenthe object and the own vehicle. Particularly, the collision mitigationapparatus 1 of the present embodiment is configured to, in the presenceof axial misalignment of the radar where a mounting angle of themillimeter-wave radar 2, which corresponds to a direction of the centeraxis of the radar, horizontally or vertically deviates from apredetermined mounting angle which corresponds to a forward direction ofa straight line passing through both the center of the front and thecenter of the rear of the own vehicle and being parallel to a roadsurface, prevent different objects from being misrecognized as the sameobject.

The collision mitigation apparatus 1, as shown in FIG. 1A, includes amillimeter-wave radar 2, a monocular camera 3, a brake electroniccontrol unit (ECU) 4, an engine ECU 5, an alert unit 6, and a collisionmitigation ECU 7. In the collision mitigation apparatus 1, for example,the collision mitigation ECU 7 is communicably connected to themillimeter-wave radar 2, the monocular camera 3, the brake ECU 4, theengine ECU 5, and the alert unit 6. Configurations to implement thecommunications are not particularly limited.

The millimeter-wave radar 2 is mounted in the center (leading edge) of afront grille of the own vehicle to detect objects, such as othervehicles and pedestrians, by using millimeter waves. The millimeter-waveradar 2 transmits millimeter waves forward from the own vehicle whilescanning in a horizontal plane and receives millimeter waves reflectedback to thereby transmit transmitted and received data in the form ofradar signals to the collision mitigation ECU 7.

The monocular camera 3 includes one charge-coupled device (CCD) camera,and is arranged on the inside of a windshield of the own vehicle betweenan interior mirror of the own vehicle and the windshield. The monocularcamera 3 transmits data of captured images in the form of image signalsto the collision mitigation ECU 7. The monocular camera 3 is providedwith a function to correct for an own axial misalignment. The forwarddirection of the own vehicle substantially coincides with an axisdirection of the monocular camera 3. Therefore, an axial misalignment ofthe millimeter-wave radar 2 can be detected with respect to the axisdirection of the monocular camera 3 (i.e., a position of an objectacquired from the image).

The brake ECU 4 includes CPU, ROM, RAM, and others to control braking ofthe own vehicle. More specifically, the brake ECU 4 controls a brakeactuator (brake ACT) in response to a detection value outputted from asensor to detect a brake pedal depression amount, where the brakeactuator serves as an actuator that opens and closes a pressureincreasing control valve and a pressure reducing control valve providedin a brake hydraulic circuit. The brake ECU 4 controls the brakeactuator following instructions from the collision mitigation ECU 7 soas to increase a braking force of the own vehicle.

The engine ECU 5 includes CPU, ROM, RAM, and others to control enginestart/shutdown, a fuel injection amount, the ignition time, and others.More specifically, the engine ECU 5 controls a throttle actuator(throttle ACT) in response to a detection value outputted from a sensorto detect an accelerator pedal depression amount, where the throttleactuator serves as an actuator that opens and closes a throttle valveprovided in an air intake conduit. The engine ECU 5 controls thethrottle actuator following instructions from the collision mitigationECU 7 so as to decrease a driving force of the internal-combustionengine.

The alert unit 6, upon reception of a warning signal from the collisionmitigation ECU 7, acoustically and optically alerts a driver of the ownvehicle.

The collision mitigation ECU 7 includes CPU, ROM, RAM, and others tointegrally control the collision mitigation apparatus 1. The collisionmitigation ECU 7 acquires radar signals from the millimeter-wave radar 2and image signals from the monocular camera 3 every predetermined timeinterval based on a master clock.

(Processing)

There will now be described object detection processing to be performedin the collision mitigation apparatus 1. An object detection program,i.e., a program for the collision mitigation apparatus 1 to implementthe object detection processing, is stored in the ROM or the like of thecollision mitigation apparatus 1. The object detection processing to beperformed in the collision mitigation apparatus 1 will be described withreference to FIG. 2. FIG. 2 illustrates a flowchart of the objectdetection processing to be performed in the collision mitigationapparatus 1 every predetermined time interval.

First, in the collision mitigation processing, as shown in FIG. 2, thecollision mitigation ECU 7 detects an object based on a radar signaltransmitted from the millimeter-wave radar 2 (i.e., detectioninformation from the millimeter-wave radar 2) (step S110). Morespecifically, based on the radar signal, the collision mitigation ECU 7calculates (or determines) a linear distance from the own vehicle to theobject and a horizontal azimuth angle of the object (i.e., an angularposition of the object from the forward direction of the own vehicle).

Based on these calculated values, the collision mitigation ECU 7, asshown in FIG. 3, calculates or determines position coordinates (X- andY-coordinates) of the object in the XY-plane as a detection point Pr ofthe object in the XY-plane. The X-axis of the XY-plane represents avehicle-widthwise direction (transverse direction) of the own vehicle,and the Y-axis of the XY-plane represents a vehicle-lengthwise direction(forward direction) of the own vehicle.

A reference point Po of the XY-plane is set at a nose (or front end) ofthe own vehicle, on which the millimeter-wave radar 2 is mounted. Thedetection point Pr is a relative position of the object with respect tothe reference point Po. FIG. 3 illustrates an example of an objectlocated forward of and to the right of the own vehicle. Additionally, instep S110, the collision mitigation ECU 7 may calculate, in addition tothe detection point Pr of the object, a relative speed and the like ofthe object with respect to the own vehicle. In the following, the objectdetected in step S110 (information about the object detected based onthe detection information from the millimeter-wave radar 2) will bereferred to as a “radar object.”

Subsequently, as shown in FIG. 3, the collision mitigation ECU 7 definesan error region 21 a centered at the detection point Pr calculated instep S110 (step S120). More specifically, the error region 21 a has atwo-dimensional extension (specified by AO) centered at the detectionpoint Pr, where an extension of the error region 21 a in the X-axisdirection represents a range of assumed error around the X-coordinate ofthe detection point Pr and an extension of the error region 21 a in theY-axis direction represents a range of assumed error around theY-coordinate of the detection point Pr. These ranges of assumed errorare predetermined based on the characteristics of the millimeter-waveradar 2.

Subsequently, the collision mitigation ECU 7 detects an object based onan image signal transmitted from the monocular camera 3 (i.e., acaptured image from the monocular camera 3) (step S130). Morespecifically, the collision mitigation ECU 7 applies image analysis tothe captured image represented by the image signal to identify anobject. This identification may be implemented by matching processingwith prestored object models.

An object model is prepared for each object type, such as a vehicle, apedestrian, or the like, which allows not only determination of thepresence of an object, but also identification of its object type. Thecollision mitigation ECU 7 determines a Y-coordinate of the object inthe XY-plane based on a vertical position of the object in the capturedimage, and a horizontal azimuth angle of the object (an angular positionfrom the forward direction of the own vehicle) based on a horizontalposition of the object in the capture image.

As the object is located more distant from the own vehicle in theforward direction of the own vehicle, that is, as the Y-coordinate ofthe object is increased, a lower end of the object tends to be locatedat a higher position in the captured image. This allows the Y-coordinateof the object to be determined based on the lower end position of theobject in the captured image. In such a specific manner, however,inaccurate detection of the lower end position of the object will leadsto lower accuracy of detecting the Y-coordinate of the object.

In addition, a horizontal displacement of the object from the focus ofexpansion (FOE) of the monocular camera 3 tends to increase with anincreasing angular displacement (inclination) of the object from theforward direction of the own vehicle (specifically, a line of X=0). Thisallows a horizontal azimuth angle of the object to be determined basedon an angle of a line passing through the reference point Po and theobject with respect to the line of X=0 and a distance to a vertical linepassing through the center of the object.

As such, in step S130, the collision mitigation ECU 7 determines theY-coordinate and the horizontal azimuth angle (angular position) of theobject in the XY-plane as the detection point Pi of the object in theXY-plane, as shown in FIG. 3. The detection point Pi of the objectrepresents a relative position of the object with respect to thereference point Po. In the following, the object detected in step S130(the object detected based on the captured image from the monocularcamera 3) will be referred to as an “image object.”

Subsequently, as shown in FIG. 3, the collision mitigation ECU 7 definesan error region 22 centered at the detection point Pi calculated in stepS130 (step S140). More specifically, the error region 22 has atwo-dimensional extension centered at the detection point Pi, where anextension of the error region 22 in the Y-axis direction represents arange of assumed error around the Y-coordinate of the detection point Piand an extension of the error region 22 in the horizontal azimuth angledirection represents a range of assumed error around the horizontalazimuth angle of the detection point Pi. These ranges of assumed errorare predetermined based on the characteristics of the monocular camera3.

Subsequently, the collision mitigation ECU 7 performs axial misalignmentcorrection processing (step S150). In the presence of axialmisalignment, the axial misalignment correction processing is performedto correct the size of the error region 21 a.

In the misalignment correction processing, as shown in FIG. 4, thecollision mitigation ECU 7 calculates an amount of axial misalignment(step S210), where a positional relationship between the radar and thecaptured image (i.e., an error between a radar coordinate system and acaptured-image coordinate system) is estimated. For example, a locationof a roadside object, such as guardrail, and its direction of movementare detected by the millimeter-wave radar 2 to determine a tilt of theroadside object arrangement with respect to the forward direction of theown vehicle and a difference in direction of the movement, based onwhich what degree of axial misalignment is occurring can be recognized.

Subsequently, the collision mitigation ECU 7 determines whether or not ahorizontal axial misalignment is occurring (step S220). If an amount ofaxial misalignment is equal to or greater than a threshold (say onedegree or so), it is determined that a horizontal axial misalignment isoccurring.

If it is determined that no horizontal axial misalignment is occurring(step S220; NO), the process flow ends. If it is determined that ahorizontal axial misalignment is occurring (step S220; YES), a relativespeed of the object with respect to the own vehicle is calculated (stepS225).

In step S225, the relative speed of the object with respect to the ownvehicle is calculated based on a detection result acquired from themillimeter-wave radar 2. In the present embodiment, the relative speedas the object moves away from the own vehicle is defined as “positive”,and the relative speed as the object approaches the own vehicle isdefined as “negative”.

Subsequently, the collision mitigation ECU 7 determines whether or notthe relative speed of the object is negative (step S230). If therelative speed of the object is negative (step S230; YES), the collisionmitigation ECU 7 makes a judgment on a direction of the axialmisalignment (step S240). If the axial misalignment is a rightward axialmisalignment (step S240; YES), the collision mitigation ECU 7 defines anerror region for the negative relative speed and the rightward axialmisalignment (step S250).

As shown in FIG. 5, when axial misalignment is occurring, the errorregion 21 a for the detection point of the millimeter-wave radar 2 isnarrowed as compared to when no axial misalignment is occurring (i.e., anormal situation). That is, AO as shown in FIG. 3 is set to a smallervalue.

In the presence of axial misalignment, as shown in FIG. 5, the width ofthe error region 21 a for a negative relative speed is set to a smallervalue than that of the error region 21 a for a positive relative speed.It can be seen that the width of the error region 21 b for a negativerelative speed as shown in FIG. 6 is set less than that of the errorregion 21 c for a positive relative speed as shown in FIG. 7.

In addition, in the presence of axial misalignment, the width of theerror region 21 a for the detection point of the millimeter-wave radar 2is corrected depending not only on the relative speed, but also on thedirection and amount of the axial misalignment. That is, as shown inFIG. 8, the width of the error region 21 a is decreased with increasingamount of the axial misalignment (or with increasing distance from theorigin as shown in FIG. 8).

In FIG. 8, the axial misalignment angle and the error region are definedas “positive” in the vehicle-widthwise (laterally) right direction. Thatis, the error region 21 a is corrected or modified such that the rightside portion of the error region 21 a is narrowed with increasing amountof the rightward axial misalignment while the left side portion of theerror region 21 a is not narrowed even with increasing amount of therightward axial misalignment. Conversely, the error region 21 a iscorrected or modified such that the left side portion of the errorregion 21 a is narrowed with increasing amount of the leftward axialmisalignment while the right side portion of the error region 21 a isnot narrowed even with increasing amount of the leftward axialmisalignment.

More specifically, for example, as shown in FIG. 9, given an amount ofthe rightward axial misalignment denoted by α, the width of the rightside portion of the corrected error region 22 d is corrected to Δθ-αwhile the width of the left side portion of the corrected error region22 d is kept at Δθ.

As such, in step S250, a correction amount, which is determined bycombining a map for correcting the width of the error region 21 adepending on the relative speed, as shown in FIG. 5, and a map forcorrecting the width of the error region 21 a depending on the amount ofthe axial misalignment, is applied to the error region 21 a to acquire acorrected error region 21 a. Also in steps S260, S320, S330 describedlater, the error region is defined using similar maps to those used instep S250.

More specifically, in step S240, if the axial misalignment is a leftwardaxial misalignment (step S240; NO), then the collision mitigation ECU 7defines an error region for the negative relative speed and the leftwardaxial misalignment (step S260). If the relative speed of the object iszero or positive (step S230; NO), then the collision mitigation ECU 7makes a judgment on the direction of the axial misalignment (step S310).

If the axial misalignment is a rightward axial misalignment (step S310;YES), then the collision mitigation ECU 7 defines an error region forthe positive relative speed and the rightward axial misalignment (stepS320). If the axial misalignment is a leftward axial misalignment (stepS310; NO), then the collision mitigation ECU 7 defines an error regionfor the positive relative speed and the leftward axial misalignment(step S330).

Thereafter, the process flow ends. Subsequently, returning to FIG. 2,the collision mitigation ECU 7 determines whether or not there is anoverlap of the radar error region 21 a and the error region 22 in theXY-plane (step S160).

If in step S160 it is determined that there is an overlap of the radarerror region 21 a and the error region 22, then the collision mitigationECU 7 determines that the radar object and the image object are the same(step S170). In this case, a position of the object determined the samein the XY-plane is specified by the Y-coordinate of the detection pointPr of the radar object and the horizontal azimuth angle of the imageobject.

Subsequently, the collision mitigation ECU 7 calculates a degree ofconfidence in determination that the radar object and the image objectare the same (step S180). In the present embodiment, the degree ofconfidence is defined by an angle difference between the horizontalazimuth angle of the detection point Pr of the radar object and thehorizontal azimuth angle of the detection point Pi of the image object.Such a degree of confidence increases with decreasing angle difference.

If it is determined in step S160 that there exists no overlap of theradar error region 21 a and the error region 22, then the collisionmitigation ECU 7 determines that the radar object and the image objectare not the same, that is, they are different objects. Then, the processflow proceeds to step S190.

Subsequently, the collision mitigation ECU 7 performs collisionmitigation control based on the position of the detected object and thedegree of confidence (step S190). For example, if the own vehicle islikely to collide with the object, the collision mitigation ECU 7transmits a warning signal to an alert unit 6 to alert the driver. Ifthe own vehicle is more likely to collide with the object, the collisionmitigation ECU 7 instructs the engine ECU 5 to decrease a driving forceof an internal-combustion engine and/or instructs the brake ECU 4 toincrease a braking force of the own vehicle.

In addition, the collision mitigation ECU 7 changes control aspectsdepending on the degree of confidence. For example, for a high degree ofconfidence, a control initiation timing is advanced as compared to acontrol initiation timing for a low degree of confidence.

In the present embodiment, the collision mitigation ECU 7 corresponds toan object detection apparatus of the present invention. FIG. 1Billustrates a functional block diagram of the collision mitigation ECU7. Various implementations of these blocks described herein can berealized in processor, in software, or in any combination thereof. Thecollision mitigation ECU 7 includes, as functional blocks, a firstregion definition unit 701, a second region definition unit 702, anaxial misalignment detection unit 703, and a relative speed acquisitionunit 704, a region size modification unit 705, and a determination unit706. The first region definition unit 701 performs steps S110-S120. Thesecond region definition unit 702 performs step S130-S140. The axialmisalignment detection unit 703 performs step S210. The relative speedacquisition unit 704 performs step S225. The region size modificationunit 705 performs steps S230-S330. The determination unit 706 performssteps S160-S170.

In the collision mitigation apparatus 1 configured as above, thecollision mitigation ECU 7 determines whether or not axial misalignmentis occurring, where the axial misalignment represents a deviation of thereference direction of the millimeter-wave radar 2 from the referencedirection of the axis of the monocular camera 3. In the presence ofaxial misalignment, the collision mitigation ECU 7 modifies the size ofthe first region. If it is determined that there is an overlap of thefirst and second regions in the XY-plane, then the collision mitigationECU 7 determines that the first object and the second object are thesame.

With the collision mitigation apparatus 1 configured as above, in thepresence of axial misalignment, the size of the first region ismodified, which can modify the determination as to whether or not thereis an overlap of the first and second regions. This allows for moreaccurate determination as to whether or not the first and second objectsare the same.

In addition, with the collision mitigation apparatus 1 configured asabove, in the presence of axial misalignment, the collision mitigationECU 7 narrows the first region. That is, since, in the presence of axialmisalignment, non-identical objects are more likely to be mistakenlyrecognized as the same, narrowing the first region can preventnon-identical objects from being mistakenly recognized as the same.

Therefore, with the collision mitigation apparatus 1 configured asabove, the determination as to whether or not the first and secondobjects are the same can be made more accurately.

In the collision mitigation apparatus 1, the collision mitigation ECU 7,in the presence of axial misalignment, acquires information about thedetermination as to whether the reference direction of the monocularcamera 3 is rightward or leftward misaligned with the referencedirection of the millimeter-wave radar 2, and narrows one of the rightside and left side portions of the first region that is situated in thedirection that the axial misalignment is occurring.

Since, in the presence of axial misalignment, different objects presentin the direction that the axial misalignment is occurring are morelikely to be mistakenly determined as the same, one of the right sideand left side portions of the first region that is situated in thedirection that the axial misalignment is occurring is narrowed. With thecollision mitigation apparatus 1 having such a configuration, thedetermination as to whether or not different objects are the same can bemade more accurately.

In the collision mitigation apparatus 1, the collision mitigation ECU 7acquires, as a relative speed, a speed difference between the first orsecond object and the own vehicle, and when the relative speed isnegative, narrows the first region as compared to when the relativespeed is negative.

With the collision mitigation apparatus 1 configured as above, when therelative speed is negative, that is, when the own vehicle is approachingthe object, the first region is narrowed, which can prevent differentobjects from being mistakenly recognized as the same. This configurationcan prevent a malfunction of the vehicle control caused by mistakenlyrecognizing different objects as the same.

In addition, in the collision mitigation apparatus 1, the collisionmitigation ECU 7 defines a certain range of angles centered at anazimuth angle of the first object with respect to the reference point asthe width of the first region, and modifies the size of the first regionby modifying only the width of the first region.

With the collision mitigation apparatus 1 configured as above, only thewidth of the first region is modified, where the determination as towhether or not different objects are the same is susceptible to theaxial misalignment. Therefore, the determination as to whether or notdifferent objects are the same can be kept unchanged in the going away(or radial) direction without being affected by the axial misalignment.

Other Embodiments

The present invention is not in any way limited to the above embodiment.Reference numerals and signs used in the above description of theembodiment are appropriately used in the claims as well. The referencenumerals and signs are used for easy understanding of the presentinvention, and should not be construed as limiting the technical scopeof the present invention. The functions of a single component may bedistributed to a plurality of components, or the functions of aplurality of components may be integrated into a single component. Atleast part of the configuration of the above embodiments may be replacedwith a known configuration having a similar function. At least part ofthe configuration of the above embodiments may be removed. At least partof the configuration of one of the above embodiments may be replacedwith or added to the configuration of another one of the aboveembodiments. While only certain features of the invention have beenillustrated and described herein, many modifications and changes willoccur to those skilled in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes as falling within the true spirit of the invention.

It should be appreciated that the invention is not to be limited to thecollision mitigation apparatus 1 disclosed above and that the presentinvention can be implemented in numerous ways, including as a systemthat includes the collision mitigation apparatus 1 as a component, aprogram for enabling a computer to function as the collision mitigationapparatus 1, a storage medium storing such a program, a collisionmitigation method and the like.

In the above embodiment, the map for correcting the width of the errorregion 21 a depending on the relative speed and the map for correctingthe width of the error region 21 a depending on the amount and directionof the axial misalignment are applied in combination. Alternatively,either one of these maps may be applied to acquire the corrected errorregion 21 a.

1. An object detection apparatus mounted in a vehicle, comprising: afirst region definition unit configured to define a first object regionincluding a first detection point, the first detection pointrepresenting a relative position of a first object detected based oninformation acquired by a radar with respect to a reference point in anXY-plane, the reference point representing a position of the vehicle, anX-axis direction of the XY-plane being a vehicle widthwise direction,and a Y-axis direction of the XY-plane being a vehicle lengthwisedirection; a second region definition unit configured to define a secondobject region including a second detection point, the second detectionpoint representing a relative position of a second object detected basedon an image captured by a monocular camera with respect to the referencepoint in the XY-plane; an axial misalignment detection unit configuredto detect the presence or absence of axial misalignment that representsa deviation of a direction of an axis of the radar from a referencedirection; a region size modification unit configured to, in thepresence of the axial misalignment, modify the size of the first region;and a determination unit configured to determine whether or not there isan overlap of the first and second object regions in the XY-plane, andif it is determined that there is an overlap of the first and secondobject regions in the XY-plane, then determine that the first and secondobjects are the same, wherein the region size modification unit isconfigured to, in the presence of the axial misalignment, narrow thefirst region.
 2. (canceled)
 3. The apparatus according to claim 1,wherein the axial misalignment detection unit is configured to, in thepresence of the axial misalignment, acquire information as to whether areference direction of the monocular camera is rightward or leftwardmisaligned with a reference direction of the radar, and the region sizemodification unit is configured to, in the presence of the axialmisalignment, narrows one of right side and left side portions of thefirst region that is situated in the direction that the axialmisalignment is occurring.
 4. The apparatus according to claim 1,further comprising a relative speed acquisition unit configured toacquire, as a relative speed, a speed difference between the first orsecond object and the own vehicle, wherein the region size modificationunit is configured to, when the relative speed is negative, narrow thefirst region as compared to when the relative speed is positive.
 5. Theapparatus according to claim 1, wherein the first region definition unitis configured to define a range of angles including an azimuth angle ofthe first object with respect to the reference point as a width of thefirst region, and the region size modification unit is configured tomodify the size of the first region by modifying only the width of thefirst object region.
 6. An object detection apparatus mounted in avehicle, comprising: a first region definition unit configured to definea first object region including a first detection point, the firstdetection point representing a relative position of a first objectdetected based on information acquired by a radar with respect to areference point in an XY-plane, the reference point representing aposition of the vehicle, an X-axis direction of the XY-plane being avehicle widthwise direction, and a Y-axis direction of the XY-planebeing a vehicle lengthwise direction; a second region definition unitconfigured to define a second object region including a second detectionpoint, the second detection point representing a relative position of asecond object detected based on an image captured by a monocular camerawith respect to the reference point in the XY-plane; an axialmisalignment detection unit configured to detect the presence or absenceof axial misalignment that represents a deviation of a direction of anaxis of the radar from a reference direction; a region size modificationunit configured to, in the presence of the axial misalignment, modifythe size of the first region; a determination unit configured todetermine whether or not there is an overlap of the first and secondobject regions in the XY-plane, and if it is determined that there is anoverlap of the first and second object regions in the XY-plane, thendetermine that the first and second objects are the same; and a relativespeed acquisition unit configured to acquire, as a relative speed, aspeed difference between the first or second object and the own vehicle,wherein the region size modification unit is configured to, when therelative speed is negative, narrow the first region as compared to whenthe relative speed is positive.